Heat recovery device and corresponding manufacturing process

ABSTRACT

A heat recovery device comprises a body inwardly delimiting an exhaust gas circulation passage and a heat exchanger. The heat exchanger includes a casing, a plurality of exhaust gas circulation tubes and at least one grate arranged in the proximal opening of the casing. The grate comprises a wall in which orifices are arranged for receiving tubes. The grate also has an upright edge protruding toward an inside of the heat exchanger, the upright edge being rigidly attached to the casing. The wall of the grate has, around the orifices, a planar surface turned toward the body. The body has an opening delimited by a flat edge pressed against the planar surface. The planar surface and the flat edge are rigidly attached to one another to be tight with respect to exhaust gases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. non-provisional application claiming the benefit of French Application No. 1762294, filed on Dec. 15, 2017, which is incorporated herein by herein in its entirety.

FIELD OF INVENTION

The invention generally relates to heat recovery devices for exhaust lines.

BACKGROUND OF THE INVENTION

Motor vehicle exhaust lines may include heat exchangers of the type shown in FIG. 1. Such a heat exchanger 1 comprises a plurality of exhaust gas circulation tubes 3. These tubes 3 are held at each of their longitudinal ends by a grate 5. A casing 7 is placed around the tubes 3 and grates 5. The tubes 3, the grates 5, and the casing 7 are attached to one another by brazing in a furnace.

Each grate 5 includes an upright edge 9 oriented toward an outside of the heat exchanger 1, to be attached on a body 11, shown in FIG. 2. The body 11 is, for example, integrated into a three-way valve making it possible to orient the exhaust gases selectively either toward the heat exchanger 1 or toward a bypass pipe of the heat exchanger 1. An end rim 13 of the upright edge 9 must be far enough away from the junction between the grate 5 and the casing 7 so as not to cause the braze securing the grate 5 to the casing 7 to melt during the welding of the grate 5 on the body 11.

The grate 5 has a generally rectangular shape. It may be formed from a flat metal sheet, the sides of which are folded down to give it a basin shape, and thus to create the upright edge 9. The metal sheet is next pierced to create orifices for receiving the tubes 3.

During the shaping of the flat metal sheet, the material is compressed at each corner of the upright edge 9. The surface condition inside the four corners is not good. Folds can be seen both inside and outside the basin.

Thus, the shaping of the grate 5 does not make it possible to have a good surface condition, or good dimensional allowances, in each corner of the upright edge 9.

Furthermore, it is difficult to obtain good flatness of each of the sides of the upright edge 9. This is due to the resilient return of the material in the four corners.

Furthermore, as visible in FIG. 2, the exchanger 1 can be attached to a barrel stretcher 15 arranged in the body 11. The upright edge 9 is inserted inside the barrel stretcher 15.

Although the barrel stretching is obtained by an elongation of the material and not by compression, the edges of the barrel stretcher 15 are absolutely not planar, due to the resilient return of the material during the shaping. The edges of the barrel stretcher 15 are not perpendicular to the plane of the opening delimited in the body 11, the undercut angle being approximately 2°.

Thus, the play between the upright edge 9 of the grate 5 and the barrel stretcher 15 is not constant, and may be greater than 0.5 mm on average.

It is possible to consider butt welding the upright edge 9 and the barrel stretcher 15, in the configuration shown in FIG. 2.

In the exhaust field, the welding method traditionally used is MAG (Metal Active Gas). With such a welding method, the significant play between the upright edge 9 and the barrel stretcher 15 may generate defects, or even holes.

For lap welding, it would be necessary to have the upright edge 9 and the barrel stretcher 15 go past one another. Yet the length of the upright edge 9 is limited by the fact that the compression of the material in the corners becomes impossible past a certain limit.

Likewise, the barrel stretcher 15 has a maximum length, related to the acceptable maximum elongation of the material.

Furthermore, the MAG method has certain known flaws, the most significant of which is deforming the parts to be welded, because these parts are heated to a high temperature, and locally.

This flaw is particularly critical when the heat exchanger 1 must be rigidly attached to a valve body, which must have a good final geometry in order for the axis of the flap to be able to rotate without interference with the valve body, and for the valve to have a good sealing level.

In this context, the invention aims to propose a heat recovery device that does not have the above flaws.

SUMMARY OF THE INVENTION

The invention relates to a heat recovery device for an exhaust line, the device comprising a body inwardly delimiting an exhaust gas circulation passage, and a heat exchanger, the heat exchanger comprising:

a casing having a proximal edge delimiting a proximal opening;

a plurality of exhaust gas circulation tubes, extending inside the casing;

at least one grate arranged in the proximal opening, the at least one grate comprising a wall in which orifices are arranged, each exhaust gas circulation tube having a proximal end engaged in one of the orifices and attached to the at least one grate, the at least one grate further having an upright edge extending around the wall and protruding from the wall toward an inside of the heat exchanger, the upright edge being rigidly attached to the casing;

the wall of the at least one grate having, around the orifices, a planar surface turned toward the body;

the body having a body opening delimited by a flat edge pressed against the planar surface; and

the planar surface and the flat edge being rigidly attached to one another to be tight with respect to exhaust gases.

Thus, in the invention, the at least one grate is turned in a direction opposite FIG. 1. This makes it possible to make the connection between the body and the grate at the planar surface of the grate surrounding the receiving orifices of the tubes. It is therefore no longer necessary to perform barrel stretching around the opening of the body, the connection between the body and the grate being done at two planar surfaces that are parallel to one another.

This advantageously makes it possible to secure the at least one grate and the body through either a brazing method or a laser welding method.

These methods are advantageous, since they do not require considerable heating of the parts, and therefore minimize the risk of deformation of the body.

Obtaining good flatness of the planar surface of the at least one grate and the flat edge of the body is easier than monitoring the geometry of the barrel stretching or the upright edge on the device of FIGS. 1 and 2.

Furthermore, the height of the upright edge is less significant than in FIGS. 1 and 2, since it is not necessary to extend the latter to the free edge of the barrel stretcher. It is only necessary to provide the junction with the casing of the heat exchanger. The manufacture of the at least one grate is easier, and the deformations are less pronounced.

The heat recovery device may also have one or more of the features below, considered individually or according to all technically possible combinations:

the planar surface and the flat edge are rigidly attached to one another by laser welding or by brazing;

the upright edge of the at least one grate is rigidly attached to the proximal edge of the casing, the wall of the at least one grate being offset toward an outside of the casing;

the planar surface has a closed contour and has a width of at least two millimeters;

the casing includes a central tubular part having a first straight section, the proximal opening having a second section greater than the first straight section;

the proximal edge of the casing is connected to the central tubular part by a tubular segment that flares from the central tubular part, the tubular segment delimiting a heat transfer fluid circulation channel along the at least one grate;

the casing has a heat transfer fluid inlet and a heat transfer fluid outlet, the heat transfer fluid inlet being arranged in the central tubular part, the central tubular part having a zone protruding toward the outside of the casing extending from the heat transfer fluid inlet to the heat transfer fluid circulation channel along the at least one grate;

the exhaust gas circulation tubes have protuberances forming spacers maintaining a determined spacing between the exhaust gas circulation tubes, and between the exhaust gas circulation tubes and the casing, the protuberances in contact with the casing all being located outside the heat transfer fluid circulation channel along the grate;

the planar surface extends in a first plane, the orifices being surrounded by a ridge adjacent to the planar surface, the ridge extending in a second plane parallel to the first plane and offset toward the inside of the heat exchanger relative to the first plane.

According to a second aspect, the invention relates to a method for manufacturing a heat recovery device having the above features,

assembling the casing, the exhaust gas circulation tubes and the at least one grate to one another by brazing; and

attaching the planar surface of the at least one grate and the flat edge of the body to one another by laser welding or by brazing.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will emerge from the detailed description thereof provided below, for information and non-limitingly, in which:

FIG. 1 is a cross-sectional view of a heat exchanger not according to the invention;

FIG. 2 is a sectional view of one end of the heat exchanger of FIG. 1, attached on a body;

FIG. 3 is an exploded view of heat exchanger of a heat recovery device according to the invention;

FIG. 4 is a longitudinal sectional view of the heat exchanger of FIG. 3, in the assembled state;

FIG. 5 is a sectional view of one end of the heat exchanger of FIGS. 3 and 4, attached on a body;

FIG. 6 is a perspective view of the heat exchanger of FIGS. 3 to 5;

FIG. 7 is a bottom view of the heat exchanger, for an alternative embodiment;

FIG. 8 is an enlarged sectional view of part of one of the grates of the heat exchanger of FIGS. 3 and 4; and

FIG. 9 is a perspective view of the grate of FIG. 8.

DETAILED DESCRIPTION

The heat recovery device 17 is provided to be integrated into an exhaust line, typically an exhaust line of a vehicle equipped with a heat engine. The vehicle is, for example, a motor vehicle, typically a car or truck.

The heat recovery device 17 is provided to recover part of the heat energy from the exhaust gases circulating in the exhaust line. The heat energy thus recovered is used on board the vehicle, for example to accelerate the temperature increase of the heat engine, or to heat the passenger cab.

The heat recovery device 17 shown in FIGS. 3 to 5 comprises a body 19 (FIG. 5) inwardly delimiting an exhaust gas circulation passage 21, and a heat exchanger 23.

The body 19 has an opening 25, through which the circulation passage 21 communicates with the heat exchanger 23.

The body 19 is, for example, a valve body. In this case, the valve is typically a three-way valve, the body 19 having at least one exhaust gas inlet and two outlets, all communicating fluidly with the circulation passage 21. The inlet is in fluid communication with a collector capturing the exhaust gases at the outlet of the combustion chambers of the heat engine. One of the outlets constitutes the opening 25 and communicates with the exhaust gas circulation side of the heat exchanger 23. The other outlet emerges in a bypass pipe of the heat exchanger. In FIG. 5, only one opening 25 has been shown.

Alternatively, the body 19 is an exhaust gas circulation pipe, the heat exchanger being mounted in a bypass on said pipe.

As illustrated in FIGS. 3 to 5, the heat exchanger 23 comprises a casing 27, and a plurality of exhaust gas circulation tubes 29, extending inside the casing 27.

The tubes 29 communicate fluidly with the circulation passage 21 through the opening 25.

The casing 27 has a proximal edge 31, delimiting a proximal opening 33.

It also includes a distal edge 35, delimiting a distal opening 37. The proximal edge 31 and the distal edge 35 have closed contours.

The heat exchanger 23 also includes at least one grate 39, arranged in the proximal opening 33. The grate 39 comprises a wall 41 in which orifices 43 are arranged.

Each tube 29 has a proximal end 45, arranged in one of the orifices 43 and attached to the grate 39.

Advantageously, the heat exchanger 23 comprises another grate 47 arranged in the distal opening 37. The other grate 47 comprises a wall 49 in which orifices 51 are arranged. Each tube 29 has a distal end 53 engaged in one of the orifices 51 and attached to the other grate 47.

Typically, the grate 39 and the other grate 47 are identical in all points. Only the grate 39 will therefore be described below in detail.

Preferably, the tubes 29 are rectilinear, and extend longitudinally from the proximal end 45 to the distal end 53.

For example, the tubes 29 have, in a transverse plane perpendicular to the longitudinal direction, a substantially rectangular section, constant over the entire longitudinal length of the tube 29. The section is elongated along a transverse direction T. The longitudinal L and transverse T directions are shown in FIG. 3.

Each tube 29 therefore has two large faces 55, 57, opposite one another, and connected to one another by sheared edges 59. The large faces 55, 57 extend substantially in planes containing the longitudinal L and transverse T directions. These planes are perpendicular to an elevation direction E, embodied in FIG. 3.

Advantageously, the tubes 29 are all stacked along the elevation direction. In other words, the heat exchanger 23 in a transverse plane comprises no more than a single tube.

Each tube 29 therefore extends practically over the entire transverse width of the heat exchanger 23. The tubes 29 are stacked such that the large base 55 of a given tube is placed across from the large base 57 of the tube immediately below it in the stack along the elevation direction.

Fins 62 are placed inside each tube 29 to promote heat exchanges on the gas side. The fins 62 are, for example, made in the form of a metal sheet folded in an accordion and inserted inside the tube 29.

The orifices 43 and 51 of the grates 39 and 47 have a shape conjugated with that of the tubes 29. They therefore have a transversely elongated shape and extend over practically the entire width of the grate. They are arranged in a single column.

The grate 39 comprises an upright edge 60, extending around the wall 41 and protruding from the wall 41 toward the inside of the heat exchanger 23.

In the illustrated example, the wall 41 is substantially rectangular, with rounded corners. As a result, the upright edge 60 includes two segments 61 that are substantially parallel to one another and extend along the transverse direction T, and two segments 63 that are substantially parallel to one another and extend along the elevation direction E. Preferably, the two segments 61 are parallel to one another and extend along the transverse direction T. Preferably, the two segments 63 are parallel to one another and extend along the elevation direction E. The segments 61 and 63 are connected to one another by curved portions.

The upright edge 60 protrudes along the longitudinal direction L. As shown in FIG. 4, the upright edge 60 is engaged in said the proximal edge 31 of the casing 27, the proximal edge 31 being pressed against an outer surface of the upright edge 60. The upright edge 60 is rigidly attached to the casing 27. More specifically, the proximal edge 31 is brazed on the upright edge 60.

The wall 41 of the grate 39 is offset toward the outside of the casing 27. The wall 41 is offset along the longitudinal direction L. This means that the wall 41 is not located inside the casing 27, but is located longitudinally past the proximal end 31 of the casing 27.

The wall 41 of the grate 39 has, around the orifices 43, a planar surface 65 turned toward the body 19.

Typically, the planar surface 65 extends in a determined plane. This plane is perpendicular to the longitudinal direction L and therefore contains the transverse direction T and the elevation direction E.

The planar surface 65 extends all around the orifices 43. The planar surface 65 therefore has a closed contour.

It has a width of at least 2 mm, for example of between 2 and 5 mm. This width is taken along a direction perpendicular to a junction line 67 between the upright edge 60 and the wall 41. In other words, this width is taken along the elevation direction E along the segment 61 of the upright edge 60, and along the transverse direction T along the segment 63 of the upright edge 60.

The planar surface 65 extends, in the illustrated example, up to the junction line 67 between the upright edge 60 and the wall 41, i.e., up to the outer edge of the wall 41.

The opening 25 is cut out in a wall of the body 19.

Typically, it is cut out in a substantially planar zone 68 of the wall, preferably with a flatness of less than 0.3. This planar zone 68 delimits, on one side, the inside of the circulation passage 21, and is therefore in direct contact with the exhaust gases. On the opposite side, it is in contact with the grate 39 of the heat exchanger.

The opening 25 of the body 19 is delimited by a flat edge 69, pressed against the planar surface 65.

The flat edge 69 is therefore in contact on one side with the planar surface 65, and on the opposite side of the planar surface 65, with the exhaust gases circulating in the body 19.

The planar surface 65 and the flat edge 69 are rigidly attached to one another to be tight with respect to the exhaust gases.

The planar surface 65 and the flat edge 69 are directly attached to one another.

The planar surface 65 and the flat edge 69 are rigidly attached to one another by laser welding or by brazing.

The planar zone 68 does not bear any relief around the flat edge 69, which makes it possible to adjust the position of the grate 39 relative to the body 19.

It should be noted that the other grate 47 is also mounted on a planar zone, such that it is possible to adjust the positions of both ends of the heat exchanger relative to one another.

The flat edge 69 has, toward the heat exchanger 23, a planar outer surface 71, pressed against the planar surface 65.

This planar outer surface 71 extends in a plane, said plane being perpendicular to the longitudinal direction L in the illustrated example.

The edge 69 has a closed contour and extends all the way around the opening 25.

The opening 25 has a size and shape such that all of the orifices 43 are located in line with said opening 25. The proximal ends 45 of the tubes 29 protrude past the grate 39, and penetrate slightly inside the opening 25, as illustrated in FIG. 5.

The heat exchanger 23 also includes a reinforcing grate 73, arranged to reinforce the connection between the tubes 29 and the grate 39. It advantageously includes another reinforcing grate 75, arranged to reinforce the connection between the tubes 29 and the other grate 47. The grate 73 and the grate 75 are identical, only the grate 73 therefore being described below.

The reinforcing grate 73 is a plate in which apertures 77 have been arranged. The apertures 77 are delimited by necks 79 (FIG. 5) and are each passed through by the proximal end 45 of one of the tubes 29. The apertures 77 are each placed across from one of the orifices 43. The necks 79 are brazed on the tubes 29. The peripheral edge 81 of the reinforcing plate, and the fields 83 located between the apertures 77, are brazed on the inner surface of the wall 41.

In the illustrated example, the proximal edge 31 and the distal edge 35 of the casing 27 are located at the two opposite longitudinal ends thereof.

The casing 27 is made in two half-shells 85, 87. The half-shells 85, 87 are secured to one another by brazing, along two longitudinal lines 89 (FIG. 6).

Each half-shell 85, 87 has a U-shaped section in a plane perpendicular to the longitudinal direction L.

The casing 27 includes a central tubular part 91 having a first straight section, the proximal opening 33 having a second section greater than the first section (FIG. 4). Likewise, the distal opening 37 has a section greater than the first section, and typically equal to the second section.

To that end, the proximal edge 31 of the casing 27 is connected to the central tubular part 91 by a tubular segment 93 that flares from the central tubular part 91.

Likewise, the distal edge 35 of the casing 27 is connected to the central tubular part 91 by another tubular segment 95 that flares from the central tubular part 91.

The tubular segment 93 delimits a heat transfer fluid circulation channel 97 along the grate 39. Likewise, the tubular segment 95 delimits a heat transfer fluid circulation channel 98 in contact with the other grate 47.

The passage section offered to the heat transfer fluid by the circulation channel 97, and also by the circulation channel 98, is significantly greater than in the heat exchanger shown in FIG. 1.

This results from several constructive arrangements of the heat exchanger.

First of all, the planar surface 65 of the wall 41 is significantly wider in the invention than in the heat exchanger of FIG. 1. Indeed, this planar surface 65 is deliberately made wider in the invention, to allow good quality tight attachment of the flat edge 69 on the planar surface 65.

Furthermore, as previously stressed, in the invention, the wall 41 is offset toward the outside of the casing 27. In the heat exchanger of FIG. 1, the wall in which the receiving orifices of the tubes are arranged is placed inside the casing 7.

This large passage section of the circulation channel 97 is particularly advantageous, since it is thus possible to increase the heat transfer fluid flow rate in contact with the grate 39. The grate 39 is typically located at the exhaust gas inlet inside the heat exchanger. Yet the heat exchangers used in exhaust lines must never come to a boil. The most critical zone with respect to boiling is always located on the exhaust gas inlet side, i.e., in the zone where the exhaust gases are hottest. In case of boiling, the heat transfer fluid turns to vapor, such that the heat exchanges at the inlet of the heat exchanger are gas-gas locally. As a result, the skin temperature of the exchanger increases quickly, and may approach the temperature of the exhaust gases (for example, around 850° C.). This risks locally creating a thermal shock and temperature gradients causing breaks, and therefore leaks, at the brazes securing the various components of the heat exchanger to one another.

It is therefore critical for a heat exchanger of this type for the heat transfer fluid flow rate in the grate 39 to be high enough to prevent any risk of boiling.

The casing 27 has a heat transfer fluid inlet 99 and a heat transfer fluid outlet 101 (FIGS. 3 and 6).

In the illustrated example, the heat transfer fluid inlet 99 and outlet 101 are arranged in the half-shell 87. The heat transfer fluid inlet 99 and outlet 101 are arranged side by side, and offset longitudinally relative to one another. The inlet 99 is located on the side of the grate 39, and the outlet 101 on the side of the grate 47. In other words, the heat transfer fluid inlet 99 is located toward the exhaust gas inlet and the heat transfer fluid outlet 101 toward the exhaust gas outlet.

The heat transfer fluid inlet 99 is located in the central tubular part 91 of the casing 27. Advantageously, and as illustrated in FIG. 7, the central tubular part 91 has a zone 103 protruding toward the outside of the casing 27, extending from the heat transfer fluid inlet 99 to the heat transfer fluid circulation channel 97, along the grate 39.

The zone 103 is not shown in FIGS. 3 to 5.

More specifically, the casing 27 has two large faces 105 and 107, which are substantially perpendicular to the elevation direction E, and two side faces 109, which are substantially perpendicular to the transverse direction T, and connecting the faces 105 and 107 to one another. The heat transfer fluid inlet 99, and typically the heat transfer fluid outlet 101, are arranged in one of the side faces 109. The protruding zone 103 is advantageously arranged on the large face 107. It has a generally triangular shape, as shown in FIG. 7. It extends transversely from the heat transfer fluid inlet 99 to the side face 109 opposite the heat transfer fluid inlet 99. Its width, taken along the longitudinal direction, decreases from the heat transfer fluid inlet 99 toward the side face 109 opposite the heat transfer fluid inlet 99.

Advantageously, the protruding zone 103 protrudes relative to a central zone 111 of the central tubular part 91 over a height substantially equal to that of the proximal end 31.

The protruding zone 103 makes it possible to collect the heat transfer fluid at the heat transfer fluid inlet 99, and to steer it preferentially toward the circulation channel 97. This promotes the cooling at the inlet of the heat exchanger and limits the risk of boiling.

Advantageously, the casing 27 also includes another protruding zone 112, extending from the heat transfer fluid outlet 101 to the heat transfer fluid circulation channel 98 along the other grate 47 (FIG. 7).

The protruding zone 112 is symmetrical with the protruding zone 103 relative to the median plane of the heat exchanger perpendicular to the longitudinal direction L.

The tubes 29 have protuberances 113 forming spacers maintaining a determined spacing between the tubes 29, and between the tubes 29 and the casing 27. These protuberances 113 are distributed on the large faces 55 and 57 of the tubes.

In the illustrated example, each of the large faces 55, 57 has around ten protuberances 113.

The protuberances 113 protrude toward the outside of the tubes 29. They are obtained by deformation of the metal making up the tube 29.

The protuberances 113 in contact with the casing 27 are all located outside the heat transfer fluid circulation channel 97 along the grate 39, and typically also outside the heat transfer fluid circulation channel 98 along the other grate 47.

This is favorable to the mechanical strength between the casing 27 and the protuberances 113.

Preferably, these protuberances are also located outside the protruding zone 103 and outside the protruding zone 112.

Typically, the protuberances 113 formed on the large faces 55 of a tube 29 are located across from the protuberances 113 formed on the large faces 57 of said same tube 29. “Across from” means opposite one another along the elevation direction E. Likewise, the protuberances 113 formed on a given tube 29 are located in the extension of the protuberances 113 of the other tubes 29 along the elevation direction E, as illustrated in FIG. 4. In other words, all of the tubes 29 have protuberances 113 having the same arrangement on their two opposite large faces 55, 57, such that said protuberances 113 form stacks in a column, along the elevation direction E. This is favorable to increasing the rigidity of the heat exchanger 23.

According to another advantageous aspect of the invention, the planar surface 65 of the grate 39 extends in a first plane P1, the orifices 43 being surrounded by a ridge 115 adjacent to the planar surface 65, the ridge 115 extending in a second plane P2 parallel to the first plane P1 and offset toward the inside of the heat exchanger 23 relative to the first plane P1. This is illustrated in FIG. 8.

The ridge 115 extends over the entire perimeter of the orifices 43. It has a closed contour, and is inwardly adjacent to the planar surface 65. It is separated from the planar surface 65 by a step.

Thus, during the brazing of the heat exchanger 23, the brazing material cannot spread over the planar surface 65. It is retained by the step separating the ridge 115 from the planar surface 65.

According to another aspect, the invention relates to the process for manufacturing the heat recovery device 17 described above.

This manufacturing process comprises the following steps:

assembly by brazing the casing 27, tubes 29 and grate 39 to one another;

attaching the planar surface 65 of the grate 39 and the flat edge 69 of the body 19 to one another by laser welding or by brazing.

Typically, in the assembly step, the other grate 47 is assembled by brazing to the casing 27 and the tubes 29.

Furthermore, the reinforcing grates 73, 75 are advantageously assembled by brazing to the tubes 29 and the grates 39, 47, in the same step.

The assembly step also makes it possible to secure the half-shells 85, 87 of the casing 27 to one another.

As described above, the casing 27 is assembled to the grate 39 by brazing of the proximal edge 31 on the upright edge 60.

The tubes 29 are assembled to one another by brazing, said brazing preferably being done at the protuberances 113.

The tubes 29 are assembled to the casing 27 by brazing of the protuberances 113 on the casing 27, and more specifically on the central tubular part 91 of the casing 27.

The brazing step is advantageously done in a furnace.

When the attachment of the planar surface 65 on the flat edge 69 is done by laser welding, this welding is done by transparency, through the flat edge 69. The weld line has a closed contour, and extends over the entire perimeter of the opening 25.

When the attachment is done by brazing, brazing paste is deposited between the flat edge 69 and the planar surface 65. The brazing paste is melted, for example, by placing the body 19 and the heat exchanger 23 in a furnace. In this case, the brazing of the planar surface 65 and the flat edge 69 can be done at the same time as the assembly by brazing of the different elements of the heat exchanger to one another.

The heat recovery device 17, and the corresponding manufacturing process, can assume multiple variants.

The grate 47 arranged in the distal opening 37 of the casing 27 could be of a different type from that arranged in the proximal opening 33.

The tubes 29 do not necessarily have the shape described above. They could a circular section, an oval section, or any other appropriate section. These tubes are not necessarily rectilinear, but alternatively are curved. In this case, the distal opening 37 of the casing 27 is not necessarily placed longitudinally across from the proximal opening 33.

The heat transfer fluid is typically a liquid. Alternatively, it is another type of fluid.

The heat exchanger 23 is not necessarily symmetrical relative to a median transverse plane of the heat exchanger. It may not include a circulation channel 98 of the heat transfer fluid in contact with the other grate 47 and/or not include a protruding zone 112.

The wall 41 of the grate 39 may have all types of shapes. It is not necessarily rectangular. Alternatively, the wall 41 is circular, or elliptical, or has any other appropriate shape.

In this case, the opening 25 arranged in the body 19 also does not have a rectangular shape. It typically has a shape corresponding to the shape of the grate 39, and more particularly to the shape of the wall 41.

To attach the grate 39 to the casing 27, the upright edge 60 is not necessarily engaged inside the proximal edge 31 of the casing 27. Alternatively, it is the proximal edge 31 of the casing 27 that is engaged in the upright edge 60 of the grate 39.

The casing 27 is not necessarily made up of two half-shells 85, 87 assembled to one another. It could be obtained by rolling a metal sheet around the longitudinal axis, or by deforming a tube segment.

The tubes 29 may be arranged in all types of different ways inside the heat exchanger 23. In particular, it is possible to place several tubes 29 next to one another transversely and not just one as described above.

The planar surface 65 does not necessarily extend in a single plane. It may include several planar zones, arranged in several planes parallel to one another or tilted relative to one another. In these cases, the flat edge 69 has substantially the same shape as the planar surface 65. In any case, the flat edge 69 and the planar surface 65 are in contact with one another over a zone with a closed contour surrounding the opening 25 and surrounding all of the orifices 43, 51. This zone is wide enough to allow the attachment of the planar surface 65 and the flat edge 69 to one another, preferably by laser welding or by brazing.

Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure. 

1. A heat recovery device for an exhaust line, the device comprising: a body inwardly delimiting an exhaust gas circulation passage; and a heat exchanger comprising: a casing having a proximal edge delimiting a proximal opening; a plurality of exhaust gas circulation tubes extending inside the casing; at least one grate arranged in the proximal opening, the at least one grate comprising a wall in which orifices are arranged, each exhaust gas circulation tube having a proximal end engaged in one of the orifices and attached to the at least one grate, the at least one grate further having an upright edge extending around the wall and protruding from the wall toward an inside of the heat exchanger, the upright edge being rigidly attached to the casing; the wall of the at least one grate having, around the orifices, a planar surface turned toward the body; the body having a body opening delimited by a flat edge pressed against the planar surface; and the planar surface and the flat edge being rigidly attached to one another to be tight with respect to exhaust gases.
 2. The device according to claim 1, wherein the planar surface and the flat edge are rigidly attached to one another by laser welding or by brazing.
 3. The device according to claim 1, wherein the upright edge of the at least one grate is rigidly attached to the proximal edge of the casing, the wall of the at least one grate being offset toward an outside of the casing.
 4. The device according to claim 1, wherein the planar surface has a closed contour and has a width of at least two millimeters.
 5. The device according to claim 1, wherein the casing includes a central tubular part having a first straight section, the proximal opening having a second section greater than the first straight section.
 6. The device according to claim 5, wherein the proximal edge of the casing is connected to the central tubular part by a tubular segment that flares from the central tubular part, the tubular segment delimiting a heat transfer fluid circulation channel along the at least one grate.
 7. The device according to claim 6, wherein the casing has a heat transfer fluid inlet and a heat transfer fluid outlet, the heat transfer fluid inlet being arranged in the central tubular part, the central tubular part having a zone protruding toward an outside of the casing extending from the heat transfer fluid inlet to the heat transfer fluid circulation channel along the at least one grate.
 8. The device according to claim 6, wherein the plurality of exhaust gas circulation tubes have protuberances forming spacers maintaining a determined spacing between the plurality of exhaust gas circulation tubes, and between the plurality of exhaust gas circulation tubes and the casing, the protuberances in contact with the casing all being located outside the heat transfer fluid circulation channel along the at least one grate.
 9. The device according to claim 1, wherein the planar surface extends in a first plane, the orifices being surrounded by a ridge adjacent to the planar surface, the ridge extending in a second plane parallel to the first plane and offset toward the inside of the heat exchanger relative to the first plane.
 10. The device according to claim 1, wherein the body opening is cut out in a wall of the body.
 11. A process for manufacturing a heat recovery device for an exhaust line, the process comprising the following steps: providing a body inwardly delimiting an exhaust gas circulation passage and a heat exchanger that includes a casing having a proximal edge delimiting a proximal opening, a plurality of exhaust gas circulation tubes extending inside the casing, at least one grate arranged in the proximal opening, the at least one grate comprising a wall in which orifices are arranged, each exhaust gas circulation tube having a proximal end engaged in one of the orifices and attached to the at least one grate, the at least one grate further having an upright edge extending around the wall and protruding from the wall toward an inside of the heat exchanger, the upright edge being rigidly attached to the casing; the wall of the at least one grate having, around the orifices, a planar surface turned toward the body; the body having a body opening delimited by a flat edge pressed against the planar surface; assembling the casing, the plurality of exhaust gas circulation tubes and the at least one grate to one another by brazing; and attaching the planar surface of the at least one grate and the flat edge of the body to one another by laser welding or by brazing to be tight with respect to exhaust gases. 